This invention relates to an ignition timing control method for internal combustion engines.
A known method of controlling the ignition timing of an internal combustion engine, such as disclosed in Japanese Provisional Patent Publication (Kokai) No. 54-43649, includes calculating ignition timing in dependence upon the operating parameters of the engine and determining the ignition timing by driving a counter from a predetermined crank angle position on the basis of the calculated results. A problem encountered with this conventional method is that if the counter takes too long to count the clock pulses applied thereto up or down, a sudden change in the rotational speed of the engine can no longer be followed up, thus making it impossible to achieve precise control of ignition timing. In other words, the longer the counting time, the higher the probability that fluctuations take place in the engine rotational speed from the time the counting starts to the time it ends, thus resulting in degraded accuracy of the ignition timing control.
Another ignition timing control method for an internal combustion engine described, for example, in Japanese Provisional Patent Publication (Kokai) No. 56-92353, includes calculating ignition timing and simultaneously checking the status of a counter whenever a signal indicative of engine revolution, such as a signal indicative of crank angle position, is generated, resetting the status of the counter whenever the value of the count remaining therein exceeds a certain value, and causing the counter to perform the counting operation anew. The disadvantage with this method wherein ignition timing is being calculated each time the engine revolution signal is generated is that these calculations do not allow calculations for other control operations to be executed.